<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        
    </style>
</head>
<body>
    
</body>
<script>
    
    var a;
    console.log(a)
    a = 10;
    console.log(a)
    var b = a;
    console.log(b);
    var c = a + b;
    console.log(c);
    var d = c > a;
    console.log(d);

    // a = a + 1
    // a += 1;
    // a *= 2;
    // a /= 3;
    // a %= 3;

    console.log(a);

    // 计算规则等同于算术运算符



</script>
</html>